Nanobody-enabled structural biology: By rigidifying flexible regions and obscuring aggregative surfaces, nanobody complexes warrant conformationally uniform samples that are key to protein structure determination by X-ray crystallography. The elucidation of the first GPCR structure in its active state using a conformationally selective Nanobody demonstrates the power of the Nanobody platform to generate diffracting quality crystals of the most challenging targets including membrane proteins, flexible proteins, aggregating proteins and protein-protein complexes.